1. Field
The present disclosure relates to a semiconductor device, and in particular, relates to technology effective when applied to a semiconductor device including a high-resistance resistive element.
2. Related Art
A power device such as an insulated gate bipolar transistor (IGBT) or power MOSFET is utilized in many fields, such as a motor controlling inverter, a power supply application of a flat panel display (FPD) such as a large capacity plasma display (PDP) or liquid crystal panel, or an inverter for a household electrical appliance such as an air conditioner or lighting.
A high voltage integrated circuit is used in the drive and control of this kind of power device. In recent years, owing to the advances in large scale integrated circuit (LSI) technology, high voltage integrated circuits of breakdown voltage classes from 100V to 1,200V, used in power supplies from consumer power supplies of 100V and 200V AC to commercial power supplies of 400V AC and the like, have been put to practical use.
A resistive element formed of a highly resistive polysilicon film is often included as a multiple floating field plate (MFFP) or resistive field plate (RFP) in a voltage withstanding structure portion of a place bearing breakdown voltage in a high voltage integrated circuit. As the capacitive field plate or resistive field plate has a function of relaxing electrical field concentration in a depletion layer of a semiconductor surface, high breakdown voltage can be stably secured.
Various structures of this kind of field plate have been reported. For example, a field plate structure wherein a resistive field plate is formed utilizing a diffusion region of a semiconductor layer surface, rather than the resistive field plate being formed of a thin film resistance layer, is disclosed in Patent Literature (“PTL”) 1 (J-PA-2013-187240). Also, a field plate structure wherein a spiral groove is provided in a semiconductor layer, and a resistive field plate formed of a thin film resistance layer is embedded across an insulating film in the spiral groove, is disclosed in PTL 2 (J-PA-1992-332173). Also, a two-layer field plate structure, wherein a resistive field plate is formed of metal layers of concentric circle form and a thin film resistance layer connecting the metal layers, is disclosed in PTL 3 (J-PA-2003-008009).
Herein, when providing a resistive field plate in the voltage withstanding structure portion of a high voltage integrated circuit, the coercive force of the potential with respect to the depletion layer of the semiconductor layer surface is strong, and reliability is high compared with that of a capacitive field plate, but the leakage current when a high voltage is applied is from several microamps to several tens of microamps, which is large compared with that of a capacitive field plate. The leakage current being large means that the leakage current from a high voltage terminal to a ground terminal in the high voltage integrated circuit is large, and the power consumption of the integrated circuit increases. Therefore, a reduction in leakage current is demanded when using a resistive field plate in the high voltage withstanding structure portion.
In order to reduce the leakage current, it is sufficient to increase the total resistance value by simply increasing the number of turns of the resistive field plate, thus increasing the effective length. However, an existing resistive field plate is such that the planar size increases in accordance with the number of turns, together with which the semiconductor chip, that is, the high voltage integrated circuit, also increases in size, because of which the chip acquisition rate obtainable from one semiconductor wafer decreases, and cost increases.
Therefore, the inventors have contrived the disclosure focusing on an existing resistive field plate being configured of only a thin film resistance layer or a diffusion resistance region.